NMR studies of I. Photodamaged DNA duplexes, II. Sodium concentrations in septic mouse and III. Two iron chelates as potential brain MRI contrast agents

DNA photoproducts induced by UV irradiation have been linked to skin cancer. Trans-syn-I and trans-syn-II cyclobutane thymine dimers are two minor DNA photoproducts that have unusual structural features that can be used to probe structure-activity relationships in mutagenesis. To better understand the structure and properties of trans-syn-I and trans-syn-II containing duplex DNA, NMR solution-state structures of duplex DNA dodecamers containing trans-syn-I and trans-syn-II cyclobutane thymine dimers and their parental duplex were determined. Also, magnetization transfer and diffusion NMR methods were used to measure the imino proton exchange time in these duplexes. The 3D models revealed that the introduction of trans-syn-I and trans-syn-II dimer causes significant distortions of the DNA backbone. Trans-syn-I dimer causes distortions mostly to the 5′ side of the dimer, while trans-syn-II dimer causes distortions mostly to the 3′ side of the dimer. The structural distortions in the trans-syn-II duplex are more severe than those in the trans-syn-I duplex. Both the 3D models and the imino proton exchange rates indicate that the hydrogen bonding between the thymine residues of the dimer and the complementary adenosine residues are reduced and/or distorted in both the trans-syn-I and trans-syn-II duplexes.; The second part of this dissertation concerns two medically related NMR studies. In the first, tissue compartment-specific sodium concentrations were measured in the muscle of septic and control mice in vivo by 23Na NMR. The chemical shift reagent TmDOTP5− was used to resolve the intra- and extracellular sodium NMR signals. No significant differences in Na content in either compartment were observed between the septic and control mice. In the second study, two iron complexes, Fe(III) tris(2-mercaptobenzyl)amine and Fe(III) tris(2-hydroxybenzyl)amine, were synthesized and evaluated as potential blood brain barrier permeable MRI contrast agents. Fe(III) tris(2-mercaptobenzyl)amine was found to be highly unstable in solution, while Fe(III) tris(2-hydroxybenzyl)amine was stable. The relaxivity of Fe(III) tris(2-hydroxybenzyl)amine was determined to be 0.776 s−1mM−1, yet its brain uptake was found to be negligible as revealed by biodistribution study. Thus, neither complex was promising as a blood brain barrier permeable MRI contrast agent.